Can somebody explain bandstacked LNBs? (re: tuning horizontal transponders)

[sofakng]

Can anybody explain the difference between a bandstacked LNB and one that is not?

I'm trying to learn a bit more about DVB systems and I'm a bit confused on this...

For example, I believe Dish Network uses Ku-Hi band with bandstacking. This means that horizontal transponders must (???) be converted to vertical transponders before being tuned? (ie. subtracting the horizontal frequency from 25600 then using it as a vertical transponder)

 

[Mr Tony]

a bandstacked LNB takes the horizontal polarity frequencies and puts them higher than the vertical (stacking them) and making it vertical

advantage....can use a satellite splitter to run multiple receivers off the dish
disadvantage...some receivers dont work with them real well

Dish Network's DishPro system does use bandstacking. There are also C-Band and KU-Band LNB's that are stacked. As example the C-Band takes the horizontal and "shifts" the frequency 600 mhz lower. If you use the "normal" LNB frequency of 5150 all your horizontals will be 600 mhz lower than what they should be.

If your receiver cannot blind scan it properly just take the frequency and subtract it from 24600 and make it vertical. So 12000 H 30000 will become 12600 V 30000

Non-bandstacked LNB's require a line from the receiver to the LNB (or multiswitch if more than 2 receivers)

 

[catamount]

Lots of threads on this, just do a search for bandstacked. I believe it is 24600 minus horz. freq. = vertical

This works for dishnetwork bandstacked and some other LNB's. When I have used one I just blindscan vertical transponders.

Starchoice bandstacked LNBs do not work with 24600 minus horizontal for some reason.

Catamount

 

[Tron]

With bandstacked LNBs, both horizontal and vertical polarities are available at all times over a single cable. There is no 13V/18V polarity switching. Just make sure that all devices and cables in your signal path are capable of handling the higher frequency range (~2.2 GHz for bandstacked vs. ~1.5 GHz for voltage switched polarity)...

 

[sofakng]

Thanks! I've been reading more and more and I think I understand most of this.

For example, DBS (Dish Network) operates their satellites on a frequency range of 12200 MHz to 12700 MHz. Our LNBs downconvert this to 950 - 2150 MHz (so it can travel further down coaxial cable, etc).

Ku-Band (?) has an LOF (Local Oscillating Frequency) of 11250. To determine the frequency on the coax cable the formula is <satellite frequency> - <LOF>. So a satellite operating at 12224 MHz will be sent over coaxial at 974 MHz.

Is that right so far?

Here's my question... how does the LOF switch between the low-range (950-1450 MHz) and high-range (1650-2150 MHz). Most tuners have settings for LOF low, high, and switch.

Do these values even apply to Dish Network?

 

[Mr Tony]

DBS has a LO frequency of 11250
KU is 10750

some receivers will scan an IF frequency range of 950-2150. Bandstacked LNB's are set up (on KU) as vertical (the actual vertical stuff) is from 11700-12200 and the bandstacked portion (horizontal) is from 12400 to 12900. Take the frequency from 24600 and make it vertical. Whats interesting on the bandstacked is the Horizontal goes from highest to lowest frequency wise

My Pansat when blind scanning bandstacked LNB's scans the IF frequency so it will start at 1550 on the horizontal side and scans til 2150 then scans vertical from 950-1500

 

[Cadsulfide]

Another advantage to bandstacked lnb's is you can keep them heated up all the time with power insertion, less drift. Feeding multiple receivers is also simpler.

 

[sofakng]

Thanks so much for all of the help!

One last question...

What does "LOF SW" (or LOF Switch) mean and how does it relate to bandstacked dishes?

For example, most DBS receivers (or applications) have three settings:

LOF (Low)
LOF (High)
LOF SW

I understand that bandstacked can have a LOF from 11250 to 14350 so would that be the LOF Low and High values? What about the switch value?

 

[SatelliteAV]

LOF SW is the frequency that receiver switches between the High LO and the Low LO frequencies.

Typically a bandstacked LNBF has a single LO frequency, so there is no LOF SW.

 

[sofakng]

Oh, OK. So a typical bandstacked LNBF just operates at 11250 MHz?

How does a LOF SW work in other receivers? For example, if the value of LOW SW is 17000 MHz, does that mean any frequence above that will go to the LOF High?

 

[SatelliteAV]

An bandstacked LNBF comes in many designs. The application determines the assigned LO frequency. For example: Dish Network has a very unique bandstack method where the LO is 14350 for even transponders and 11250 for odd transponders.

Correct! An LOF SW triggers the Switch between low and high LO bands.

 

[AcWxRadar]

SOFAKNG,

Take the most common example of bandstacking technology - from Dish Network. DN has two systems - Legacy and Dish Pro.

Legacy systems still work with 13V/18V signals to switch the desired polarity reception at the LNBF unit. One local oscillator is used to extract the signal from both polarities and the switching is accomplished by selecting which pickup probe is used for the desired polarity. If the LH polarity probe is selected, the IF frequency coming down the cable and into the receiver is 950-1450 MHz. If the RH polarity probe is selected, the IF frequency coming down the cable and into the receiver is also 950-1450 MHz. Since they are using the same frequency band, both polarities (signals) cannot occupy the cable at the same time, so you must either have two cables or select only one polarity at a time.

Dish Pro systems use two local oscillator frequencies, one specific local oscillator for each pick up probe. These local oscillators and pick-up probes are active all the time, so no switching signals are sent to the LNBF to alter between the RH and LH polarities. The detection is now accomplished within the receiver itself. Since there are two L.O.'s, the IF frequency is unique for each polarity. One band (950 - 1450 MHz) represents the LH circular polarity signals and the other band (1650 - 2150 MHz) represents the RH circular polarity signals.

Now, you can utilize ONE cable to carry both LH and RH polarity signals simultaneously without cross talk interference. The receiver knows to look for the RH (12200 - 12700) polarity signals in the IF frequency range of 950 - 1450 MHz and the LH (12200 - 12700) polarity signals in the IF frequency range of 1650 - 2150 MHz. They are now separated by their frequencies and can co-exist on the same cable at the same time. Everything to differentiate the polarities will be accomplished within the receiver.

Now, I am not absolutely certain of this, but I believe that the L.O. for the RH polarity signals is 11250 MHz and the L.O. for the LH polarity signals is 10550 MHz. But, if this is right, it is only right for DN's circular satellites. The theory is correct, but I may have the numbers wrong.

Regardless of any number errors, which are not critically important for this discussion, the overall scoop is covered.

EDIT: I should add a novelty way of remembering the association between circular and linear polarities. RH (right hand circular) = Vertical/linear and LH (left hand circular) = Horizontal/linear.
The phrase is: I can drive an RV with my Left Hand. RV = Right hand + Vertical. Left Hand = LH = Left + Horizontal. Rather trite but it works.

RADAR

 

[sofakng]

OK - So in a DishPro LNB, there is no low and high band, right? It's all one band? (11250 - 14350 MHz)

...so that means there is also no LOF Switch?

 

[SatelliteAV]

The Dishpro series LNBFs have high band and a low band outputs, but they use DiSEqC 2.0 switching protocol to change between LO 11250 on even transponders to LO 14350 for odd transponders. Dishpro LNBFs do not use the LOF SW (LO frequency switch point) function.

 

[sofakng]

Errr, now I'm confused again.

I thought DPP LNBFs combine both horizontal and vertical transponders onto the same cable? I also thought that there were two LOFs operating (one for the horizontal and the other for the vertical) but then the result was having everything on one cable without any DiSEqC switching. (unless you want to switch satellites)

 

[Mr Tony]

Why do we have a thread this long about the specs on a Dish Network LNB's when last I checked the only freebie on those satellites is Dish 101 channel?

 

[sofakng]

I just like learning about this kind of stuff. I'm a software developer and recently started looking into how MPEG transport streams were assembled and how they are used for DVB systems, etc.

There are quite a few more free channels on the eastern arc satellites though... I've found the NASA channel, Pentagon channel, and a bunch of others but I really haven't been watching anything. Like I said, I'm just fooling around trying to learn.

I'm very sorry if this thread is inappropriate.

 

[AcWxRadar]

Why do we have a thread this long about the specs on a Dish Network LNB's when last I checked the only freebie on those satellites is Dish 101 channel?

Ice,

I picked the DN LNBFs (Dish Pro and Dish Pro Plus) for an example because the information is more readily available through DN application and engineering notes.

RADAR

 

[AcWxRadar]

The Dishpro series LNBFs have high band and a low band outputs, but they use DiSEqC 2.0 switching protocol to change between LO 11250 on even transponders to LO 14350 for odd transponders. Dishpro LNBFs do not use the LOF SW (LO frequency switch point) function.

Brian,

I wasn't certain of the LO for the odd TPs - being 14350. I see that with this LO the 12200 downlink frequency actually becomes the highest IF frequency (2150 MHz) and the higher 12700 downlink actually becomes the lowest IF frequency (1650 MHz). This is since you subtract the downlink from the LO instead of the LO from the downlink.

However, I am confused because DN application notes state that the two IF frequencies are co-existing on a single cable simultaneously. So why would they send a DiSEqC 2.0 signal to switch this? I was under the impression that the receiver did the switching between the two polarities internally and they only sent out the DiSEqC 2.0 signals to the LNBF to select (switch) between the different satellites when using multi-sat LNBFs like the Dish Pro Twin?

Is the information from DN just being vague on this technical point for the sake of simplicitiy of discussion?

RADAR

 

[AcWxRadar]

Errr, now I'm confused again.

I thought DPP LNBFs combine both horizontal and vertical transponders onto the same cable? I also thought that there were two LOFs operating (one for the horizontal and the other for the vertical) but then the result was having everything on one cable without any DiSEqC switching. (unless you want to switch satellites)

Sofakng,

This is my understanding as well. I retrieved the information from a couple of DN app notes. However, if they (DN) are not stating the entire details, I may be wrong. They may be doing so just out of simplicity in their engineering notes. They do show a drawing of the signal from a spectrum analyzer with both bands on the same cable, at the same time, but again, that may be just out of simplicitiy for their discussion... I don't know.

The main thing is that they are not using 13VDC and 18VDC for any of this switching. That is certain and the main reason why they can extend the length of the cable.

RADAR